1. Field of the Invention
This invention relates to a semiconductor laser array which emits a plurality of laser lights having different wavelengths and which is suitable for use in transmission or processing of multi-wavelength-light information.
2. Description of the Prior Art
Conventional semiconductor laser arrays of this kind are known in which a plurality of semiconductor lasers having a distributed feed back (DFB) structure of distributed Bragg reflector (DBR) are formed on a substrate in a monolithic construction manner and the diffraction gratings for the respective lasers are formed with different pitches, and which thereby emits a plurality of laser light beams having different wavelengths. In this type of laser array, however, the difference between the wavelengths of the lights emitted from the lasers is small and is at most several nanometers if the laser array is designed to make the characteristics of the lasers uniform.
A known type of laser array designed to emit a plurality of laser lights having wavelengths greatly different from each other based on forming an active layer of each laser in a quantum well structure is proposed in U.S. Pat. No. 4,817,110, particularly in the statement between line 16 in col. 21 and line 6 in col. 24 of the specification thereof. This laser array is constructed in such a manner that a plurality of semiconductor lasers having active layers having a quantum well structure are arranged on a substrate so that internal losses or reflection losses of the respective layers are different from each other. For example, as stated at lines 59 to 62 in col. 23 of the same specification, the mirror loss of the respective laser may be varied by varying the reflectivity of the mirror of the respective laser by such as a method of end facet coating.
However, the mirror loss of this laser array is not determined with respect to the oscillation wavelength of each laser light, and it is not assured that all the lasers can effect oscillation under suitable conditions. For this reason, there is a risk of a reduction in the emission efficiency or dispersion of the characteristics of the lasers.